There is an absolute requirement for boron in many plants. In vascular plants, for example, boron is essential for the structure and function of cell walls, and may also be important in regulating hormones. In many animals, boron apparently also plays an important role, especially in calcium and magnesium metabolism. In chickens, for example, boron deficiency leads to poor growth and leg abnormalities in chicks, while boron supplementation produces stronger egg shells. (Mastromatto E., et al., "Summary: International Symposium on the Health Effects of Boron and its Compounds", Environ Health Perspect., 1994 November; 102, 7:139-41).
In humans boron offers significant benefits with respect to bone and joint health. Supplemental boron has also been shown to improve mental functions such as eye-hand coordination, attention, perception, short-term and long-term memory, and likely promotes healthy hair, skin and nails. (McCoy et al, Environ. Health Persepct., 1994 November; 102 Suppl. 7:49-53; U.S. Pat. No. 5,312,816 to Spievogel et al., issued May 17, 1994; "Newnham, Environ. Health Perspect., 1994 November; 102 Suppl., 7: 8305; Penland, J. G., Environ. Health Perspect., 1994 November; 102 Suppl., 7:65-72; Murray, T., H., "Keep bones and joints healthy with boron", Health Counselor, 1997 June-July, 32-33.
The optimum daily intake of boron in humans appears to be about 2-3 mg/day. The bioavailability of boron in both water and foods is relatively high, and in theory this optimum daily intake could be readily obtained from a high quality diet. In water, for example, about 89% of boron is absorbed, and in foods such as broccoli absorption may reach 100%. Unfortunately, however, this amount is not present in ordinary diets, as the dietary intake of boron by individuals in North America is reported to be only about 1 mg. It also turns out that boron is most helpful when magnesium levels are sufficient, and magnesium levels are notoriously deficient in modern diets.
Supplemental boron is known in many different forms. As over-the-counter supplements, for example, boron is marketed as calcium borogluconate (Now Foods, Glendale Hts., Ill.), and as boron citrate, aspartate and glycinate chelates (Twin Laboratories, Inc., Ronkonkoma, N.Y.). U.S. Pat. No. 4,849,220 to Hunt, issued Jul. 18, 1989, describes the addition of boric acid (H.sub.3 BO.sub.3) to the diet of postmenopausal women, and U.S. Pat. No. 5,312,816 to Spielvogel et al. describes dietary supplementation with Lewis-acid base boron adducts. Boron has also been given as a simple salt, such as sodium borate, or sodium tertraborate decahydrate.
These known forms of boron supplementation leave something to be desired. First, the known forms either contain or are readily hydrolyzed in the gut to boric acid. Boric acid is reactive, and tends to accumulate in tissues other than bone or joint. Second, the amount of boron made available by known supplementation is extremely high compared with normal blood values. A typical boron supplement, for example, may make almost 3 mg of elemental boron available to the tissues within a half hour after ingestion, which is about 14 times the normal total blood boron of 213 .mu.g. (Hunt, C. D., et al., "RDA Workshop: New Approaches, Endpoints and Paradigms for RDAs of Mineral Elements", American Institute of Nutrition, 1996, pp 2441S-2451 S). Third, while there is a mechanism which limits boron absorption from foods when boron intake is high, (Hunt, C. D., et al., "RDA Workshop . . . ", supra), that mechanism likely does not act to prevent the almost immediate availability of boron from currently known supplements. Fourth, it has been estimated that less than a quarter of the population takes vitamin/mineral supplements on a daily basis, so that the known forms of supplementation are unlikely to reach a high percentage of the population.
Thus, there is a continuing need to provide boron in a supplementation form in which the elemental boron is tightly bound to a ligand. Since blood boron levels are probably transiently defined by a single meal, and highly influenced by snacks, there is also a need to provide boron in conjunction with a food which is commonly eaten, preferably on a relatively frequent basis such as in a snack. Still further, there is a need to provide boron in conjunction with a source of magnesium.